Electromechanical force measuring cell

ABSTRACT

Electromechanical force-measuring cell which includes a deformation member formed of two cylindrical tubes of different diameters having a common central axis extending in direction of measurement of a force, one end of each of the tubes being adapted, respectively, to absorb an applied force and a force reactive thereto, a conical tube interconnecting the other ends, respectively, of the tubes, the other ends facing in opposite directions along the common central axis, and force-measuring means comprising a mechanical-to-electrical transducing device disposed at the respective other ends of the cylindrical tubes to which the conical tube is connected, for converting to an electrical signal a deformation produced in the deformation member by action of a force applied thereto.

[ Feb. 22,1972

[54] ELECTROMECHANICAIL FUWCE MEASURING CELL [72] Inventor: GottfriedBirkholtz, Weiterstadt, Germany [73] Assignee: Carl SchenckMaschineniabril: Gmlhllil,

Darmstadt, Germany 221 Filed: Sept. 24, 11970 [21] Appl.No.: 15,042

3,453,582 7/1969 Birkholtz ..73/l4l A UX FOREIGN PATENTS OR APPLICATIONS1,155,922 10/1963 Germany 73/141 A 1,156,580 10/1963 Germany ..73/l4l APrimary ExaminerCharles A, Ruehl Att0rneyCurt M. Avery, Arthur E.Wilfond, Herbert L, Lerner and Daniel J. Tick [5 7] ABSTRACTElectromechanical force-measuring cell which includes a deformationmember formed of two cylindrical tubes of different diameters having acommon central axis extending in direction of measurement of a force,one end of each of the tubes being adapted, respectively, to absorb anapplied force and a force reactive thereto, a conical tubeinterconnecting the other ends, respectively, of the tubes, the otherends facing in opposite directions along the common central axis, andforce-measuring means comprising a mechanical-to-electrical transducingdevice disposed at the respective other ends of the cylindrical tubes towhich the conical tube is connected, for converting to an electricalsignal a deformation produced in the deformation member by action of aforce applied thereto.

6 Claims, 2 Drawing Figures ELECTROMECHANICAL FORCE MEASURING CELL Myinvention relates to electromechanical force-measuring cell and, moreparticularly, to such cell having a deformation member formed of twocylindrical tubes of different diameters having a common central axisextending in direction of measurement of a force, an end of each of thetubes serving to absorb an applied and a reactive force, respectively,the other ends, respectively, of the tubes being interconnected by aconical tube.

Force measuring cells have been known heretofore which have deformationmembers in the form of a cylindrical tube extending coaxially to theaxis of measurement. The force being measured is applied to one end ofthe tube through a conical tube, the introduction of a reactive force tothe other end of the tube being effected through another conical tubedisposed in mirror-image relationship to the first-mentioned conicaltube with respect to a central plane extending therebetweenperpendicularly to the measurement axis. Under the applied effect of acompressive force, the wall of the cylindrical tube arches or curvesoutwardly in the shape of a barrel. This has the disadvantage that inthe individual sections of the electrical measuring elements disposed onthe outer surface thereof, such as expansive measuring strips,resistance wire windings, semiconductor measuring elements or the like,varying deformations in the tube are sensed by the measuring elementsections in accordance with their location or the outer surface of thetube, and thereby nonlinearities are produced in the measurement result.In order to prevent this from happening, in other heretofore knownforce-measuring cells, conical tubes for introducing the applied andreactive forces are disposed in a special manner, one of the conicaltubes extending within the cylindrical tube forming the deformationmember proper, and the other of the conical tubes extending on theoutside of the cylindrical tube. Under the action of an applied force,this results in a parallel displacement of the wall of the cylindricaltube in radial direction and therewith a correspondingly equal affect onthe electrical measuring element at the wall of the cylindrical tube. Ina spe cial embodiment of these known force-measuring cells, twocylindrical tubes provided with such conical force-introducing tubes asdeformation members are connected so as to conduct the applied forceserially, whereby the force-introducing tube of the one deformationmember passes or merges into the force'introducing tube of the otherdeformation member without change in direction. Such force-measuringcells are relatively complex and costly to produce.

It is an object of my invention, accordingly, to produceelectromechanical force-measuring cell which meets the same requirementswith regard to force-measuring technology as the last-mentionedheretofore known force-measuring cells but which is considerably simplerand less costly to produce than the conventional cells.

It is another object of my invention, in order to meet the high demandsimposed by measurement technology, to provide such forcemeasuring cellwith components that are assemblable without screws or similarfasteners, thereby assuring that there will be only a small temperaturegradient practically along uniform heat-conductive paths to themeasuring elements in the measurement direction, and that the assembledcell will occupy a minimum amount of space.

With the foregoing and other objects in view, I provide therefore inaccordance with my invention, electromechanical force-measuring cellcomprising a deformation member formed of two cylindrical tubes ofdifferent diameters having a common central axis extending in directionof measurement of a force, one end of each of the tubes being adapted,respectively, to absorb an applied force and a force reactive thereto, aconical tube interconnecting the other ends, respectively, of the tubes,the other ends facing in opposite direction along the common centralaxis, and force-measuring means comprising a mechanical-to-electricaltransducer disposed at the respective other ends of the cylindricaltubes to which the conical tube is connected, for converting to anelectrical signal a deformation produced in the deformation member byaction of a force applied thereto.

In accordance with another feature of the invention, the cylindricaltubes concentrically telescope one another.

In accordance with a further feature of the invention, I also provide ahollow rigid casing portion surrounding the deformation member, and acasing base located at one end of the tube adapted to absorb thereactive force being shrinkfittingly clamped between the hollow casingportion and the casing base.

In accordance with an additional feature of my invention. I

provide an annular casing cover formed as a guide membrane and havingrigid outer peripheral and inner peripheral edge portions, and aforce'introducing member located at the one end of the other tubeadapted to absorb the applied force, the force-introducing member andthe one end of the other tube being shrink-fittingly secured by theinner peripheral edge portion of the guide membrane, the out peripheraledge portion of the guide membrane being shrink-fittingly secured to thehollow rigid casing portion.

In accordance with a concomitant feature of the invention. I include anauxiliary deformation member connected in parallel force-transmittingrelationship to the first-mentioned deformation member whereby theapplied force is absorbed in part by both of the deformation members,the auxiliary deformation member being of such dimension that the partof the applied force absorbed thereby produces a deformation therein,within the measuring range and in the measurement direction, that isequal in size to the deformation produced in the first-mentioneddeformation member by the part of the applied force absorbed thereby.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin electromechanical force-measuring cell, it is nevertheless notintended to be limited to the details shown, since various modificationsand structural changes may be made therein without departing from thespirit of the invention and within the scope and range of equivalents ofthe claims.

The construction and method of operation of the invention. however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings, in which:

FIG. 1 is an axial view, partly in longitudinal section of oneembodiment of an electromechanical force-measuring cell ac cording to myinvention, showing a deformation member formed of concentricallytelescoped cylindrical tubes; and

FIG. 2 is a view similar to that of FIG. I of another embodiment of theinvention which includes an auxiliary deformation member to permit themeasurement of greater forces than with the embodiment of FIG. 1.

Referring now to the drawing, and first, particularly, to FIG. llthereof, there is shown therein a force-measuring cell according to myinvention which has a deformation member formed of two cylindrical tubes1 and 2 of different diameter, which concentrically and coaxiallytelescope one another. In operation, a force is applied in direction ofthe arrow i.c., vertically downwardly as shown in FIG. 1, along thecentral axis 3 which coincides with the measurement axis of theforce-mew suring cell of the invention. As viewed in the direction ofthe measurement axis, the respective inner ends of the tubes 1 and 2,which are disposed in opposite directions, are connected to one anotherby a conical tube 4. At the faces of the ends of the tubes 1 and 2 thatare connected to the conical tube 4 mechanical to-electrical transducingdevices or electrical measuring elements 5 and 6, such as windings ofelectrical resistance wire, electrical resistance wire, electricalexpansion measuring strips or the like, are disposed and are connectedin such manner to the adjacent surfaces of the tube ends that anydeformation of the tubes 1 and 2 or the surfaces at the adjacent endsthereof are transmitted thereto and thereby produce therein anelectrical signal corresponding to the deformation. This can be effectedin various known ways, for example by suitably varying the electricalconductivity of the measuring elements.

The other and outer end of the cylindrical tube 1 is shrinkfittinglyclamped between a rigid casing base 7 and a hollow rigid cylinder 8forming a lateral casing wall. The other and outer end of thecylindrical tube 2 as well as a force-introducing member 9 are firmlysecured by a shrink-fit in a rigid inner peripheral edge of an annularguide membrane 10 which forms a casing cover for the force-measuringcell. The annular guide membrane 10 is also provided with a rigid outerperipheral edge by which it is shrink-fitted on the upper end, as viewedin FIG. 1, of the hollow cylindrical casing portion 8.

The deformation member formed of the cylindrical tubes 1 and 2 and theconical tube 4 is preferably formed of one piece, which is capable ofbeing effected in an especially simple manner due to the ratherfavorable geometrical form thereof. The tube ends which serve tointroduce the applied force and the reactive force, advantageously bothare provided with a suitable shape, with shoulders, extensions or thelike for forming a shrink-fit joint. The symmetrical structure of thedeformation body with respect to a central plane extending horizontallyin FIG. 1 produces, in the direction of the measurement axis 3 from bothsides of the central horizontal plane, heat-conductive paths of uniformlength to the deformation body and to the measuring elements 5 and 6disposed thereon, so that a favorable temperature characteristic isafforded. In addition the space requirement for the force-measuring cellof my invention is very small, especially in the measurement directionin which, for the most part in practice, little space is available. Thisadvantage provided by the expedient construction of the force-measuringcell of my invention is further enhanced by the fact that thecylindrical tubes 1 and 2 concentrically telescope one another.

When the casing base 7 is supported on an abutment or counterbearing anda compressive force is introduced in direction of the arrow shown inFIG. 1 to the force-introducing member 9 a reactive force is introducedat the lower end of the tube 1, as viewed in FIG. 1, as theforce-introducing member is guided through the membrane 10 exactly inthe measuring direction of the axis 3 and transmits the applied force,that is to be measured, to the upper end of the tube 2, as viewed inFIG. 1. Under the action of the applied and reactive forces and due tothe connection provided by the conical tube 4, the tubes 1 and 2 becomeinclined with respect to the axis 3 i.e., the diameter of the annularface of the tube end adjacent the measuring element 5 is reduced and thediameter of the annular face of the tube end adjacent the measuringelement 6 is increased in accordance with the force being measured. Whenthe measuring elements 5 and 6 are suitably connected into anamplifying-electric circuit the electrical signals of the measuringelements 5 and 6, which are in proportion to the force applied, areamplified in a conventional manner.

When measuring a tensile force, the casing base 7 must be anchored in asuitable manner as indicated by the provision of a threaded or screwconnection 11, and the force-introducing member 9 must be connected tothe source of the applied force by a threaded, clamping or similarconnection. The operation of the force-measuring cell in such case is,nevertheless, analogous to the aforedescribed operation, the measuringelement 5 being expanded and the measuring element 6 being compressed.Obviously, the installation of the force-measuring cell in other spatiallocations for suitably anchoring the same is readily possible.

The form of the force-measuring cell of FIG. 1 permits the use thereofalso for measuring relatively high forces when suitable choice of thematerial and the thickness of the walls of the deformation member hasbeen made. The advantage of the compact construction can be maintainedalso for measuring very high forces with the embodiment of FIG. 2. InFIG. 2, the deformation member 1, 2, 4 constructed substantially as inthe embodiment of FIG. 1, is connected in parallel with an auxiliarydeforming member 12 with respect to the transmission of force therein.The deformation member 12 has substantially the shape of a hollowcylinder and is shrink-fittingly, rigidly connected through suitableshoulders, formed at both ends thereof, to the a plied force andreactive force-introducmg ends of the tubes and 1, respectively. Theforce transmission is thereby divided between both the deformationmember 1, 2, 4 and the auxiliary deformation member 12. The auxiliarydeformation member 12 is provided with such dimension that, within themeasuring range of the force-measuring cell of the invention, thedeformation path in measurement direction produced therein by the partof the force absorbed thereby is the same, respectively, as thedeformation path produced in the deformation member 1, 2, 4 by the partof the force absorbed by the latter member. In order to equalize orbalance manufacturing tolerances and to afford trouble-free transmissionof the force and the deformation path, consequently, to the deformationmember 1, 2, 4, an incompressible intermediate layer 2a of suitablematerial is interposed between the two deformation members.Incompressible materials which can be used for the layer 2a arehardenable multicomponent resins or plastic materials, metals such aslead, for example, care being taken that the surfaces thereof have noroughness which could cause pointlike stressing, and incompressibleliquids such as oil, for example, suitable containment thereof beingnecessary, however.

Iclaim:

l. Electromechanical force-measuring cell comprising a deformationmember formed of two cylindrical tubes of different diameters having acommon central axis extending in the direction of measurement of aforce, one end of each said tubes being adapted, respectively, to absorban applied force and a force reactive thereto, a conical tubeinterconnecting the other ends, respectively, of said tubes, said otherends facing in opposite directions along said common central axis, andforce-measuring means comprising a mechanical-to-electrical transducingdevice disposed at the respective other ends of said cylindrical tubesto which the conical tube is connected for converting to an electricalsignal a deformation produced in the deformation member by action of aforce applied thereto.

2. Electromechanical force-measuring cell according to claim 1 whereinsaid cylindrical tubes concentrically telescope one another.

3. Electromechanical force-measuring cell according to claim 1 includinga hollow rigid casing portion surrounding said deformation member, and acasing base located at one end of said hollow casing portion, the oneend of the tube adapted to absorb the reactive force beingshrink-fittingly clamped between said hollow casing portion and saidcasing base.

4. Electromechanical force-measuring cell according to claim 3 includingan annular casing cover formed as a guide membrane and having rigidouter peripheral and inner peripheral edge portions, and aforce-introducing member located at the one end of the other tubeadapted to absorb the applied force, the force-introducing member andsaid one end of said other tube being shrink-fittingly secured by saidinner peripheral edge portion of said guide membrane, said outerperipheral edge portion of said guide membrane being shrinkfittinglysecured to said hollow rigid casing portion.

5. Electromechanical force-measuring cell according to claim 1 includingan auxiliary deformation member connected in parallel force-transmittingrelationship to said first-mentioned deformation member whereby theapplied force is absorbed in part by both of said deformation members,said auxiliary deformation member being of such dimension that the partof the applied force absorbed thereby produces a deformation therein,within the measuring range and in the measurement direction, that isequal in size to the deformation produced in the first-mentioneddeformation member by the part of the applied force absorbed thereby.

6. Electromechanical force-measuring cell according to claim 5 whereinsaid auxiliary deformation member is substantially tubular in shape andcoaxially surrounds the first-mentioned deformation member.

1. Electromechanical force-measuring cell comprising a deformationmember formed of two cylindrical tubes of different diameters having acommon central axis extending in the direction of measurement of aforce, one end of each said tubes being adapted, respectively, to absorban applied force and a force reactive theretO, a conical tubeinterconnecting the other ends, respectively, of said tubes, said otherends facing in opposite directions along said common central axis, andforce-measuring means comprising a mechanical-to-electrical transducingdevice disposed at the respective other ends of said cylindrical tubesto which the conical tube is connected for converting to an electricalsignal a deformation produced in the deformation member by action of aforce applied thereto.
 2. Electromechanical force-measuring cellaccording to claim 1 wherein said cylindrical tubes concentricallytelescope one another.
 3. Electromechanical force-measuring cellaccording to claim 1 including a hollow rigid casing portion surroundingsaid deformation member, and a casing base located at one end of saidhollow casing portion, the one end of the tube adapted to absorb thereactive force being shrink-fittingly clamped between said hollow casingportion and said casing base.
 4. Electromechanical force-measuring cellaccording to claim 3 including an annular casing cover formed as a guidemembrane and having rigid outer peripheral and inner peripheral edgeportions, and a force-introducing member located at the one end of theother tube adapted to absorb the applied force, the force-introducingmember and said one end of said other tube being shrink-fittinglysecured by said inner peripheral edge portion of said guide membrane,said outer peripheral edge portion of said guide membrane beingshrink-fittingly secured to said hollow rigid casing portion. 5.Electromechanical force-measuring cell according to claim 1 including anauxiliary deformation member connected in parallel force-transmittingrelationship to said first-mentioned deformation member whereby theapplied force is absorbed in part by both of said deformation members,said auxiliary deformation member being of such dimension that the partof the applied force absorbed thereby produces a deformation therein,within the measuring range and in the measurement direction, that isequal in size to the deformation produced in the first-mentioneddeformation member by the part of the applied force absorbed thereby. 6.Electromechanical force-measuring cell according to claim 5 wherein saidauxiliary deformation member is substantially tubular in shape andcoaxially surrounds the first-mentioned deformation member.